1. Field of the Invention
The present invention relates generally to liquid crystal displays and, more particularly, to a liquid crystal display for a windshield of an automotive vehicle.
2. Description of the Related Art
1) Liquid-Crystal. The technology of liquid-crystal is well known and extensively utilized. Calculators primarily use liquid-crystal for their numeric displays. These are know as liquid-crystal-displays (LCD). These LCD's are produced in a variety of shapes.
Since liquid crystal molecules respond to an external applied voltage, liquid crystal can be used as an optical switch, or light valve. A common arrangement is two parallel glass plates, each with a polarizing film on its outer side. The space between the plates is filled with the liquid crystal polymer. The technical designation for the most commonly used liquid crystal type is twisted nematic (TN), and the twist refers to the tendency of the polymers to form chains that rotate from one side of the gap between the plates to the other side. This alignment can be changed with an external electric field, allowing the polarization of incoming light to be changed.
Light passing through one of the polarizers, then through the cell (the arrangement of plates, and liquid crystal), has its polarization direction rotated, following the physical rotation of the liquid crystal. When viewed, the cell is clear, or transmitting. A transparent electrical conductor is deposited on the inner surfaces of the glass plates, and patterned into a series of mutually perpendicular lines. If a voltage is placed across the cell gap by addressing the appropriate line on each side of the cell,the liquid crystal reorients to follow the applied electric filed,and the material is "untwisted". As long as the voltage is present, the passage of light will be blocked by the exit polarizer. When the voltage is turned off, the liquid crystal returns to its original state, and the pixel (defined viewing area) becomes clear again. Typical voltages and currents are quite low, which is why liquid crystal displays have been incorporated in battery-operated equipment,and in other applications where power consumption is an issue.
2) Heads-Up-Display (HUD). Originally developed for the use of the military in fighter aircraft. Now HUD has been translated to broader commercial use in automotive vehicles.
A HUD works by reflecting an image off the windshield into the drivers line of sight. The image presented to the driver is information pertaining to the vehicle's status such as speed. This allows the driver to easily determine the vehicle speed while looking out through the windshield. Thus allowing the driver to maintain their heads up position while driving instead of breaking their view of the road to determine speed. A light intensive image is necessary so that it is able to reflect off the windshield. The equipment necessary to generate the image is set below the windshield and the image generated is projected up into the windshield which in turn is reflected off the windshield and into the drivers line of vision. Sometimes special optics are used to define and focus the image so that after the image is reflected off the windshield the driver is presented with a clear and coherent image.